At some point cloaked in the (recent) mists of time, Elon Musk took over the mantle of leading U.S. visionary, as is the prerogative apparently of our technology billionaires. That's in no small part because his current crop of companies—SolarCity, SpaceX and Tesla—all began to thrive. But it’s also because the South African native turned American entrepreneur has a notably offhand way of imagining a more plentiful—and beautiful—future. The man's musings about something he called the Hyperloop last summer set off a frenzy of tech blogging and tweeting. Would Musk finally solve the problem of wildly unglamorous yet vital public transportation, as he seems to have solved the conundrums of the electric car, private spaceflight and cheap solar power? (Well, not entirely, but you know what I mean.)

On August 12, after a self-professed all-nighter, Musk unveiled just what in the heck he had been talking about as the Hyperloop—with a little part-time help from engineers at Tesla and SpaceX. It turns out to be a clever kludge of ideas that have been floating around since the 19th century—all designed to take people from Los Angeles to San Francisco in 35 minutes. Take a pod that would carry passengers all in a row and put it in a tube where it can be accelerated to high speeds like a bullet in a gun. Don't make the tube a vacuum, however, since it's all too easy to mess up a vacuum-based system given nature's general abhorrence and whatnot. Nor should the tube be normal pressure either, like the pneumatic mail tubes of yesteryear, given that pushing all that air around would entail too much energy when expanded over hundreds of kilometers, not to mention an absurd amount of friction on the tube walls.

Musk's solution was to cheat: make the pair of steel tubes low pressure, roughly 100 Pascals or "1/6 the pressure of the atmosphere of Mars," he wrote in the proposal outlining the Hyperloop concept posted online. And, to get around that little problem of airflow, have the pods come equipped with a hole and a battery-powered fan and compressor so that the air in front is sucked in and then used as the traveling cushion—think air hockey—underneath the pod's 28 skis. Oh, did I not mention the Inconel skis? These struts, made from a superalloy more commonly found on spaceships and nuclear power plant steam generators—which should give you some idea of the kinds of temperatures and pressures the supermetal can withstand—help the pod glide along the tube at 1,220 kilometers-per-hour, with a boost every 110 kilometers or so from the kind of linear induction motors Tesla uses to make its amazing cars go, flattened along the walls of the tube. Those motors, and the batteries aboard the pods, would be charged up by all the efficient photovoltaics laid out atop the tube's roof, producing an estimated 57 megawatts-worth of power, or nearly three times as much as Musk calculates the Hyperloop would need to operate. "You'd have to dump the power somewhere," Musk noted in a 30-minute conference call with reporters to discuss the big idea.

Top speed could be reached in as little as 35 seconds with no life-threatening gravitational pressures on the 28 or so passengers (possibly including three "full-sized" vehicles if we want to pay for the deluxe model.) The whole multibillion dollar tube would rest on at least 25,000 six-meter-tall pylons (with dampers inside to protect against earthquakes) placed every 30 meters or so that would follow the same route as I-5, keeping land and permit-buying costs to an estimated $1 billion. Total travel time would be 35 minutes between downtown L.A. and S.F. Elon calculates your ticket on the Hyperloop would set you back about $20, though each pod would cost around $1.35 million.

So far, so good, and no violations of the laws of physics, if possibly of the laws of economics. But there are some readily apparent flaws. Even at low pressure, there's an awful lot of air resistance, a.k.a. friction, heating the air inside the tube, which is why each pod would need to carry some 800 kilograms of water on board strictly for cooling purposes (for those non-metric types that's almost a ton)—adding weight and perhaps instability, with all that water sloshing around under fast acceleration. By the end of the trip, that water would be steam and, somehow, much like Better Place's failed battery swap system, those ton-heavy cartridges of cooling water would be swapped out. That's some feat, and we might want to consider other cooling fluids.

The air skis would also start to lose their luster at lower speeds, so the pods might need wheels for takeoff and landing. The linear accelerators lining the tube would need their own battery packs, in case the electricity got cut off, so that each pod already in the system could complete its journey—and it's a little unclear (to put it kindly) what would happen if one of the pods suddenly depressurized inside this partial vacuum tube. The 1 g passenger experience also might not be for everyone (consider that roller coasters subject thrill-seekers to roughly 0.5 g), though most of that would be pressing down on the passengers as Musk noted in a conference call with reporters.

This hyper loopy concept springs from Musk's disappointment in California's high speed rail plans, which are both slower than other trains out there at an average speed of 264 kph and more expensive per mile at a total estimated bill of nearly $70 billion. Of course, that has something to do with California land prices and U.S. rules and regulations. The Hyperloop, such as it is, offers no solution to political gridlock, NIMBY-ism or high land prices. In fact, it is almost absurd to suggest that all the land that would be needed for the Hyperloop to connect L.A. and S.F. would cost just $1 billion. If the physical science of the Hyperloop is not outrageously loopy, there is a near complete vacuum on the social science side.

Ultimately, the Hyperloop could cost less than the very real world high speed rail proposal because it exists in a vacuum, a protective air cushion created by any engineering proposal that only exists on paper. I salute the innovative thinking but there's also a lack of foresight, and let's remember this is not a new idea. It is an old idea that, as even Musk admits, has never found a way to get built.

As it stands, no one actually plans to build the Hyperloop, not even Elon, though he might go so far as to fund a prototype. "I think I would have to punt it for a little bit of time," Musk mused on the conference call. "It wouldn't be immediate." Maybe one of Elon's superrich friends—Google's Sergey Brin or his PayPal co-founder Peter Thiel—could divert some of their riches from other vanity projects like Brin's lab meat or Thiel's seasteading to fund development of the Musk-mobile. "If somebody else does the demo, that'll be really awesome," Musk added, suggesting if he's the only one doing the Hyperloop, it would be pretty far down his list of tasks and might take at least a whole decade to accomplish.

That's a bit sad given that one of Scientific American's original editors, Alfred Ely Beach, built a pneumatic tube train—in 1870, under New York City. No small feat. Surely we citizens of the 21st century could build a pneumatic tube train over the I-5 highway if we really wanted to, no?

Or we could just bring back the Concorde, or some other supersonic airplane and forget about the tubes. As Musk notes "with a high enough altitude and the right geometry, the sonic boom noise on the ground would be no louder than current airliners." Maybe he'll build that instead. Or, as he wrote of figuring out real teleportation: "someone please do this."

The views expressed are those of the author(s) and are not necessarily those of Scientific American.

ABOUT THE AUTHOR(S)

David Biello

David Biello is a contributing editor at Scientific American. He has been reporting on the environment and energy since 1999.

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